Knowledge of an aircraft's trajectory, whether planned or already executed, is useful for a number of reasons. By trajectory, an unambiguous four-dimensional description of the aircraft's path is meant. The trajectory description may be the evolution of the aircraft's state with time, where the state may include the position of the aircraft (e.g. the position of the aircraft's center of mass) and, optionally, the evolution of other aspects of the aircraft's motion such as velocity, attitude and weight. Thus, the trajectory may be represented as an indication of each of these typical aircraft states at consecutive points in time during the flight. For example, the trajectory may be represented as a sequence of geometric altitudes, ground speeds and geometric bearing angles at successive points in time in the evolution of the trajectory.
Methods exist that allow aircraft trajectories to be calculated from aircraft intent. Aircraft intent is a description of how the aircraft is to be flown. For example, the aircraft intent is expressed as instructions using a formal language. The description provides a complete description of the aircraft's behavior such that all degrees of freedom of motion are defined and a unique trajectory may be calculated unambiguously from the description. The trajectory may be calculated using a trajectory computation infrastructure that, in addition to the aircraft intent data, uses a description of the aircraft performance and a description of the atmospheric conditions as further inputs. European Patent Application No. EP-A-2040137, also in the name of The Boeing Company, describes aircraft intent and trajectory computation in more detail, and the disclosure of this application is incorporated herein in its entirety by reference.
Aircraft intent allows an aircraft's trajectory to be predicted unambiguously by solving a set of differential equations that model both aircraft behavior and atmospheric conditions. The aircraft intent may be derived from flight intent, as follows. Flight intent may be thought of as a generalization of the concept of a flight plan, and reflects operational constraints and objectives such as intended or required route and operator preferences. Generally, flight intent may not unambiguously define an aircraft's trajectory, as the information it contains need not close all degrees of freedom of the aircraft's motion. Put another way, there are likely to be many aircraft trajectories that would satisfy a given flight intent. Thus, flight intent may be regarded as a basic blueprint for a flight, but lacks the specific details required to compute unambiguously a trajectory.
For example, the instructions to be followed during a standard terminal arrival route (STAR) or a standard instrument departure (SID) would correspond to an example of flight intent. In addition, airline preferences may also form an example of flight intent. To determine aircraft intent, instances of flight intent like a SID procedure, the airline's operational preferences and the actual pilot's decision making process are combined. This is because the aircraft intent comprises a structured set of instructions that are used by a trajectory computation infrastructure to provide an unambiguous trajectory. The instructions should include configuration details of the aircraft (e.g. landing gear deployment), and procedures to be followed during maneuvers and normal flight (e.g. track a certain turn radius or hold a given airspeed). These instructions capture the basic commands and guidance modes at the disposal of the pilot and the aircraft's flight management system to direct the operation of the aircraft. Thus, aircraft intent may be thought of as an abstraction of the way in which an aircraft is commanded to behave by the pilot and/or flight management system.
Aircraft intent is expressed using a set of parameters presented so as to allow equations of motion to be solved. These parameters may be ground-referenced parameters, air-referenced parameters, or a combination of both. Aircraft intent may be expressed as a full operational aircraft intent that defines completely how the aircraft is to be operated. As an alternative, the aircraft intent may be expressed as a kinematic aircraft intent in which instructions relating to the required kinematics for following a trajectory are specified (for example, to specify the three dimensional position and speed that the aircraft should follow). The theory of formal languages may be used to implement these formulations of aircraft intent: an aircraft intent description language provides the set of instructions and the rules that govern the allowable combinations that express the aircraft intent, and so allow a prediction of the aircraft trajectory.
Also, it is possible to take a description of an aircraft trajectory and calculate a corresponding operational aircraft intent. However, there may be more than one operational aircraft intent that would give rise to an aircraft trajectory.
Aircraft intent is especially useful in planning flights and missions of aircraft. Expressing aircraft intent using formal languages provides a common platform for the exchange of flight information and allows different interested parties to perform trajectory calculations.
There exist reasons why it would be advantageous to determine if an aircraft trajectory is feasible. For example, an aircraft trajectory may be described in ground referenced parameters. A check may be required to ensure that it may be flown in the current atmospheric conditions. Alternatively, the trajectory may have been calculated using previously existing atmospheric conditions, and a check is required that the same trajectory remains feasible in the current atmospheric conditions.
As another example, a specific trajectory may have been calculated for a particular aircraft type and a check is required to confirm that the specific trajectory is feasible for another aircraft type. The other aircraft may be, for example, an aircraft with lesser performance and/or agility.
A third example arises where a change in the trajectory is required. This could arise in air traffic management (ATM). Air traffic management is responsible for the safe separation of aircraft. This may be a particularly demanding task especially in congested airspaces, such as around airports. ATM decision-support tools based on accurate trajectory descriptions could allow a greater volume of aircraft to be handled while maintaining safety. It has been proposed for aircraft to file desired trajectories, for example by filing descriptions of aircraft intent. ATM should be able to compare the trajectories to determine conflicts, to amend the desired trajectories to resolve conflicts, and to inform affected aircraft of the changes to their trajectories. Then changes may be made to the desired trajectories by ATM without regard to the aircraft's performance. In this case, either the ATM or the aircraft (or both) should determine whether or not it is feasible for the aircraft to fly the amended trajectory.